Abstract
BACKGROUND: Vitamin D has been suggested to influence the immune system, and vitamin D metabolites and the vitamin D receptor (VDR) are generated and expressed in white blood cells (WBC). Moreover, vitamin D status has been associated with incidence and prognosis of some respiratory tract infections (RTI). Therefore, we investigated the effect of vitamin D(3) supplementation on WBC, acute phase reactants (APR), and the risk of developing RTIs. METHODS: A double-blinded, randomized, placebo-controlled clinical trial of 307 infertile men with multiple secondary immunological endpoints. The vitamin D(3) group (n = 151) initially received 300,000 IU (7,500 µg) cholecalciferol once - followed by 1,400 IU (35 µg) daily for 150 days. The placebo group (n = 156) did not receive active ingredients. RESULTS: At baseline, stratification into clinically relevant groups of vitamin D status (< 25; 25-50; 50-75; >75 nmol/L), showed an inverse association with total leucocyte concentrations (7.0 vs. 6.0 vs. 6.0 vs. 5.5 (10(9)/L); p = 0.007), lymphocytes (2.4 vs. 2.1 vs. 2.0 vs. 2.0 (10(9)/L); p = 0.048), CRP (2.0 vs. 1.7 vs. 1.2 vs. 1.2 (mg/L); p = 0.037), and orosomucoid (0.82 vs. 0.77 vs. 0.76 vs. 0.70 (g/L); p = 0.015). After 150 days, no differences were detected in WBC counts or APRs between the vitamin D(3) and the placebo group. However, vitamin D(3) treated men had a higher prevalence of self-reported RTIs compared with the placebo group (55% vs. 39%; p = 0.005). CONCLUSIONS: High-dose vitamin D(3) supplementation did not alter WBCs or APRs, but a higher prevalence of respiratory infections was observed in the vitamin D(3) group. Serum 25(OH)D(3) was negatively correlated with most WBCs, indicating that vitamin D status may be linked with inflammation and WBC turnover, but not an important determinant of developing RTIs. TRIAL REGISTRATION: NCT01304927 (ClinicalTrials.gov). Registered February 20, 2011.